The present invention relates to the continuous vertical top casting of a thin cast-iron tube, i.e. a tube in which the ratio of the thickness/diameter is low, less than 10%, the thickness itself not exceeding 5 mm.
More precisely, the invention relates to a tubular die for the continuous casting of a tube of this type.
According to U.S. Pat. No. 4,236,571, an installation for the continuous casting of a tube of this type comprises, below a pouring-basin provided with a lower orifice, a substantially cylindrical die which is surrounded by a cooling jacket and with a core which passes through the basin to define a tubular space for the casting of the tube, an extractor device pulling on the solidified tube step by step as it is formed.
When casting a thin-walled tube and more particularly a cast-iron tube, since the entrance to the casting space is narrow, the danger of it being obstructed by a premature partial solidification is considerable.
It has thus been proposed to provide the die with a head penetrating inside the casting orifice and thus to transfer the entrance to the tubular space to a hotter region. In certain cases, the head is a simple extension of the cylindrical body of the die. In other cases, according to a more advantageous construction, it is formed by a frustoconical projection becoming thinner in the upwards direction, which is immersed in the liquid melt inside the casting orifice.
Now it will be understood that if any obstruction of the entrance is thus virtually eliminated, there will nevertheless be formed, at certain more or less regular longitudinal intervals, corresponding to multiples of the extraction step of the solidified tube, rings of a superficial incrustation of solidified cast-iron, which are not amalgamated and not welded to the remainder of the cast-iron cast in the annular space. Although they are of slight depth, these rings may nevertheless reach half the total width of the annular space between the core and die and consequently, half the thickness of the cast tube. They thus cannot be tolerated in the production of a thin cast-iron tube of great length, since they are areas of weakness which must be eliminated by cutting up the cast tube. A total obstruction of the supply of cast-iron and an interruption of casting also occurs occasionally.